Operating on 70cms (432MHz)

Non-intensive 70cms operating without a big stationIntroduction

What
follows is my "take" on 432MHz operation over the
years. As with all my ham band operation I have never been one
for large antennas, high power linears and the likes. Most times
I operate with 5-10W and frequently with far less. Clearly,
if you have a stack of large yagis on a 50m tower and 1kW erp
you will be able to make contacts over distances I could not
imagine and access modes such as EME that simply would not be
possible with QRP. What I want to show is that even with a very
modest antenna and a few watts (or milliwatts) the band is still
capable of great results and enormous fun.

The 1970s

My very first experience on
the band was back in the early 1970s when I first came up to
Cambridge. Having no equipment for the band I built a passive
tripler using a varicap diode and simple down-converter based
on a design in VHF Communications magazine. With my homebrew 2m AM transmitter
which put out 500mW I was able to achieve 100mW output on 70cms.
On receive the passive mixer had about 6-7dB loss, so it was
not very sensitive, but it worked. With just a 4 el yagi in
my loftspace I made my first tentative contacts with local stations.
Greater fun was to be had out portable and in contests the best
DX with just 100mW AM and this very small yagi was all the way
up to Yorkshire (G3NHE) at around 160kms. In those days a call
on ANY evening from a hilltop would guarantee several contacts
up to 50kms away even with such low power and simple antennas:
activity was high.

The 1980s

In the early 1980s I owned one of the first FM321 70cms synthesised
4W FM transceivers (based on an Australian UHF CB radio) and with
this plus an old Jaybeam 48el TV antenna mounted vertically on
a pole and turned by hand on the side of the house I was able
to work lots of local repeaters and some decent inter-G DX on
FM simplex when there was "a bit of a lift on". 70cms has localised lifts every few days and that was
part of the magic of the band: one day you could hear just locals
and the next (in just one direction maybe) more distant repeaters or
simplex stations could be heard or worked. Every day was different.
Occasionally the band would be wide open and some super DX could
be heard or worked.

In those days I did not have
any SSB transmitting gear on the band but I did listen in contests
and at other times and well recall hearing an OZ station running
10W to an HB9CV antenna and being a true 59+ signal on a small
indoor beam in the bedroom. The band is excellent for tropo
DXing but it is much under-used nowadays.

70cms Today

In
more recent years I have done some operation on FM (simplex
and via repeaters) from home using my vertical V2000 colinear
antenna and occasionally come on SSB using my 2m halo.
It is extremely inefficient but does match quite well and has
allowed some contacts. Using VX1 and VX2 FM handhelds some interesting
QSOs have been had when out portable on clifftops in Devon.
I am sure that with my Moxon coathanger yagi or a small HB9CV
it would be possible to achieve some quite spectacular FM simplex
DX using these little radios or similar.

In the last few months I have
tried some portable 70cms SSB/CW contest operation using my
Moxon 2el yagi and achieved some decent results. I am currently
considering the erection of a 70cms yagi and rotator at home
so that I can exploit the band for its tropo potential in lift
conditions. Based on my earlier experience I believe a reasonably
sited 70cms QRP station should be able to work 60-80kms or more on SSB/CW
in flat conditions to similarly equipped stations. Of course,
70cms experiences lots of minor tropo enhancements so if enough
stations were active the country would be criss-crossed with
QSOs most days. Sadly, activity is now very limited indeed (even
when conditions are good) outside of contests and activity nights.

70cms is an excellent band
for portable and mountain-topping operation as the antennas
are small and lightweight. See for example theSOTA
beamfor both 2m and 70cms.

Another bonus of 70cms is the
lack of interference from TVs, SMPSUs and PCs. Compared
with the HF and lower VHF bands it is positively quiet.

Finally, don't forget satellites.
I have never tried working through these on 70cms but it should
be quite possible with a modest station. Many of the many satellite's
70cm beacons are audible on a very simple antenna and receiver.

Beacons

A
useful indicator of conditions on any band are distant and semi-distant
beacons. 70cms is no exception although several UK beacons appear
to be not operational at the present time. Check the beacon
listto see what ones should be audible. It is
quite possible some will be right on or in the noise but checking
these and more distant repeaters will give you a good idea of
conditions, which can vary greatly even over a few hours.

A useful antenna for beacon
monitoring would be a big wheel such as the WiMo one shown above.
These omni-directional horizontal polarised antennas have a
few dB gain by compressing the vertical lobe. As they "see"
in all directions they allow many beacons to be checked quickly.

Conclusions

Do give 432MHz SSB or simplex
FM a go sometime
and if you think you have no suitable antenna then turn to your
wife or girlfriend's wardrobe and search out an old coat hanger.
Alternatively, a small yagi can readily be made from parts available
from the local DIY shop and turned either by hand or by the
smallest of rotators.

If you only come on for the
odd contest you will be assured of some fun and who knows you
might, like me, be persuaded to erect a more permanent beam and rotator
and find out what the band is REALLY good for. Even if you can
only run a few watts of SSB and a small beam the band has lots
to offer especially in the smallest of lifts.